There’s an old expression: “Necessity is the mother of invention.” And in the world of machinery engineering today, nowhere is that more true than with diesel engine design and development. Strict emissions limits set by the European Union and the U. S. Environmental Protection Agency have engineers scrambling to create new technologies to meet these challenging targets.
Currently, off-highway engines are transitioning from Tier 3 (Stage III A in Europe) to Interim Tier 4 (Stage III B) standards.
During a media event in Waterloo, Iowa, in June, John Deere’s engine team gave farm journalists a look at what that company’s new Interim Tier 4/Stage III B engines look like. These lower-emission 6.8-, 9.0-and 13.5-litre engines, designated PowerTech PVX and PSX models, will hit full production in January 2011.
The company decided to go its own way with the engineering direction taken on the PVX and PSX engines to meet the Stage III B requirements. It’s sticking with what it started on the current PowerTech, Stage III A engines. In short, it will use cooled exhaust gas recirculation (EGR) and exhaust filtration to meet the tougher emissions limits.
An alternative route, which some other engine manufacturers have opted for, is selective catalytic reduction (SCR). With SCR, urea injected into the exhaust stream reduces nitrogen oxide (NOx) levels. That system requires the use of a second fluid, meaning another tank that must be kept full and another cost. Although proponents of that technology claim the resulting reduction in fuel consumption offsets the cost of the urea. There are, however, reportedly still problems to work out with that technology, particularly in cold climates.
But Deere’s engine team believes evolving its existing emissions-control strategy was the best route to go. “We’re building on the same technology,” says Steve Meinzen, manager of emission technology integration. “Since we were there with Tier 3, we’re going to stay there,” adds Douglas Laudick, project manager for Deere’s Interim Tier 4 strategy.
HOW EGR WORKS
Under certain conditions, the EGR valve opens and measured amounts of cooled exhaust gas are returned to the intake manifold. This reduces the amount of oxygen in the cylinders and lowers combustion temperatures, reducing NOx levels.
This probably sounds a little familiar. It’s similar to what Detroit automakers opted for in the 1970s to meet highway emissions mandates on gasoline engines for cars and light trucks, but Deere’s EGR set up is significantly more refined.
To make the EGR strategy work, the PVX and PSX engines will use a dual turbo design. The first fixed-geometry turbo boosts intake air pressure. The second variable-geometry turbo further boosts intake pressure and mixes the recycled exhaust gas with fresh air. With two turbos sharing the job, the stress on each one is lower and blade rotation is slower, which extends their service life.
More emissions reductions happen in the exhaust filter, which has two parts: the diesel particulate filter and oxidization catalyst. Hydrocarbons and particulate matter (PM) are captured in the filter. But all this extra equipment brings up maintenance questions, such as will these filters need to be changed?
According to Deere, the filters are designed so that exhaust heat oxidizes captured particles and keeps the filter clear, giving it a very long life. But extended periods of lower engine operating temperatures could interfere with that process. To prevent that, the engine management system can detect filter restriction. When that happens, an automated injection of diesel fuel into the exhaust stream raises exhaust temperatures, which helps oxidize the trapped particles and keep the filter clear. Deere says these filters should have a minimum service interval of 4,500 operating hours.
One added advantage of having the exhaust filter is that a muffler is not required. As well, the PVX and PSX engines will offer a low-pressure fuel system to eliminate hard starting and a 500-hour oil change interval.
NEXT PHASE STARTS IN 2014
Beginning in January 2014, Final Tier 4/Stage IV standards will come into force, and the PVX and PSX engines will then have to be phased out. To say those final standards will be tough to meet is a bit of an understatement. Stage IV engines will need to have a 90 per cent reduction in PM and a 50 per cent drop in NOx over Stage III B.
And because engineers will be charting new territory to meet the Final Tier 4/Stage IV emissions requirements, there is a lot of uncertainty about what will happen after 2014. Deere’s official statement is that it will continually evaluate new technologies before committing to a Final Tier 4/Stage IV engine design.
And at the media briefing, Meinzen and Laudick acknowledged that Deere may eventually have to adopt SCR technology to hit the Final Tier 4 target. These are exciting times for engine enthusiasts.
Scott Garvey specializes in writing about tractors and farm machinery technology for publications in Canada and Great Britain. He’s also a former affiliate member of the Society of Automotive Engineers (SAE). He
farms near Moosomin, Sask.